There are conventionally known systems for providing online games to user terminals such as personal computers, smartphones, or game-dedicated terminals connected to the system via a communication line such as the Internet (see, e.g., Japanese Patent Application Publication No. 2013-066524). For example, in a system for providing services generally called cloud gaming, a server performs arithmetic processing and image processing in accordance with progression of the game based on input information sent from a user terminal, and sends the result of the processing to the user terminal in the form of a video. For another example, in a system for providing services generally called multi-player online games, a server communicates with a game-dedicated terminal or a user terminal having installed thereon dedicated software by using a dedicated protocol, thereby providing games that can be simultaneously played by many users.